How pressing is the risk? Enough, I think, to change thinking about human self-preservation fundamentally. The current state of the environment can be summarized thus:

The global population is precariously large, and will become much more so before peaking some time after 2050. Humanity overall is improving per capita production, health, and longevity. But it is doing so by eating up the planet's capital, including natural resources and biological diversity millions of years old. Homo sapiens is approaching the limit of its food and water supply. Unlike any species that lived before, it is also changing the world's atmosphere and climate, lowering and polluting water tables, shrinking forests, and spreading deserts. Most of the stress originates directly or indirectly from a handful of industrialized countries. Their proven formulas for prosperity are being eagerlyadopted by the rest of the world. The emulation cannot be sustained, not with the same levels of consumption and waste. Even if the Industrialization of developing countries is only partly successful, the environmental aftershock will dwarf the population explosion that preceded it.

Some will, of course, call this synopsis environmental alarmism. I earnestly wish that accusation were true. Unfortunately, it is the reality grounded opinion of the overwhelming majority of statured scientists who study the environment. By statured scientists I mean those who collect and analyze the data, build the theoretical models, interpret the results, and publish articles vetted for professional journals by other experts, often including their rivals. I do not mean by statured scientists the many journalists, talkshow hosts, and think tank polemicists who also address the environment, even though their opinions reach a vastly larger audience. This is not to devalue their professions, which have separate high standards, only to suggest that there are better qualified sources to consult for factual information about the environment. Seen in this light, the environment is much less a controversial subject than suggested by routine coverage in the media.

Consider, then, the assessment made through the mid 1990s by the statured scientists. Their quantitative estimates differ according to the mathematical assumptions and procedures variously used, but most still fall within limits from which trends can be projected with confidence.

By 1997 the global population had reached 5.8 billion, growing at the rate of 90 million per year. In 1600 there were only about half a billion people on Earth, and in 1940, 2 billion. The amount of increase during the 1990s alone is expected to exceed the entire population alive in 1600. The global growth rate, after reaching a peak during the 1960s, has been dropping ever since. In 1963, for example, each woman bore an average of 4.1 children. In 1996 the number had declined to 2.6. In order to stabilize the world population, the number must be 2.1 children per woman (the extra 0.1 allowing for child mortality). Long term population size is extremely sensitive to this replacement number, as shown by the following projections. If the number were 2.1, there would be 7.7 billion people on Earth in 2050, leveling off at 8.5 billion in 2150. If 2.0, the population would peak at 7.8 billion, then drop by 2150 to 5.6 billion, the total in the mid 1990s. If 2.2, it would reach 12.5 billion in 2050, 20.8 billion in 2150 and if 2.2 could miraculously be maintained thereafter, the human biomass would eventually equal the weight of the world and then, after a few millennia, expanding outward at the speed of light, it would exceed the mass of the visible universe. Even if the global birth rate were reduced drastically and immediately, say to the Chinese goal of one child per woman, the population would not peak for one or two generations. The overshoot is ensured by the disproportionate number of young people already in existence, who look to long lives ahead.

How many people can the world support for an indefinite period? Experts do not agree, but; a majority put the number variously between 4 and 16 billion. The true number will depend on the quality of life that future generations are willing to accept. If everyone agreed to become vegetarian, leaving nothing for livestock, the present 1.4 billion hectares of arable land (3.5 billion acres) would supply about 10 billion people. If humans utilized as food all the energy captured by plant photosynthesis, some 40 trillion watts, Earth could support about 16 billion people. From such a fragile world, almost all other life forms would have to be excluded.

Even if, by force majeure, the population levels off at well under 10 billion by mid century, the relatively extravagant lifestyle now enjoyed by the middle classes of North America, Western Europe, and Japan cannot be attained by most of the rest of the world. The reason is that the impact of each country on the environment is multiplicative. It is dependent, in a complex manner, on the formula called PAT: population size times per capita affluence (hence consumption) times a measure of the voracity of the technology used in sustaining consumption. The magnitude of PAT can be usefully visualized by the “ecological footprint” of productive land needed to support each member of the society with existing technology. In Europe the footprint is 3.5 hectares (a hectare is 2.5 acres), in Canada 4.3 hectares, and in the United States 5 hectares. In most developing countries it is less than half a hectare. To raise the whole world to the U.S. level with existing technology would require two more planet Earths.

It matters little that North Dakota and Mongolia are mostly empty. It makes no difference that the 5.8 billion people in the world today could be logstacked out of sight in a corner of the Grand Canyon. The datum of interest is the average footprint on productive land, which must somehow be lowered if significantly more people are to achieve a decent standard of living.

To suppose that the living standard of the rest of the world can be raised to that of the most prosperous countries, with existing technology and current levels of consumption and waste, is a dream in pursuit of a mathematical impossibility. Even to level out present‐day income inequities would require shrinking the ecological footprints of the prosperous countries. That is problematic in the market‐based global economy, where the main players are also militarily the most powerful, and in spite of a great deal of rhetoric largely indifferent to the suffering of others. Few people in industrialized countries are fully aware of how badly off the poor of the world really are. Roughly 1.3 billion people, more than a fifth of the world population, have cash incomes under one U.S. dollar a day. The next tier of 1.6 billion earn $ 1—3. Somewhat more than 1 billion live in what the United Nations classifies as absolute poverty, uncertain of obtaining food from one day to the next. Each year more than the entire population of Sweden, between 13 and 18 million, mostly children, die of starvation, or the side effects of malnutrition, or other poverty‐related causes. In order to gain perspective, imagine the response if Americans and Europeans were told that in the coming year the entire population of Sweden, or Scotland and Wales combined, or New England would die of poverty.

Of course the exemptionalists will say that new technology and the rising tide of the Free market economy can solve the problem. The solution, they explain, is straight forward: Just use more land, fertilizer, and higher yield crops, and work harder to improve distribution. And, of course, encourage more education, technology transfer, and free trade. Oh, and discourage ethnic strife and political corruption.

All that will certainly help, and should have high priority, but it cannot solve the main problem, which is the finite resources of planet Earth. It is true that only 11 percent of the world’s land surface is under cultivation. But that already includes the most arable part. The bulk of the remaining 89 percent has limited use, or none at all. Greenland, Antarctica, most of the vast northern taiga, and the equally vast ultra‐dry deserts are not available. The remnant tropical forests and savannas can be cleared and planted, but at the cost of most of the species of plants and animals in the world, with minor agricultural gain. Nearly half their expanse is underlaid by soils of low natural fertility—42 percent of the untapped area of sub Saharan Africa, for example, and 46 percent of that in Latin America. Meanwhile, cultivated and deforested lands arelosing topsoil to erosion at ten times the sustainable level. By 1989, 11 percent of the world's cropland had been classified by soil experts as severely degraded. From 1950 to the mid 1990s the area of cropland per person fell by half, from 0.23 hectare to 0.12 hectare, less than a quarter the size of a soccer field. Widespread starvation was avoided because; the Green Revolution during the same forty-year period boosted per hectare yield dramatically with new varieties of rice and other crops, better pesticide application, and increased use of fertilizer and irrigation. But even these technologies have limits. By 1985 the growth in yield slowed; that trend, when combined with the relentless growth of population, initiated a decline in per capita production. The shortfall first became apparent in the developing countries, whose grain self‐sufficiency fell from 96 percent in 1969—71, at the height of the Green Revolution, to 88 percent in 1993—95. By 1996 the world grain carryover stocks, humanity’s emergency food supply, had declined 50 percent from the all time peak reached in 1987. At the beginning of the 1990s only a handful of countries—including Canada, the United States, Argentina, the European Union, and Australia— accounted for more than three‐fourths of the world’s grain resources.

Perhaps all these signs will miraculously disappear. If not, how will the world cope? Perhaps the deserts and non arable dry grasslands can be irrigated to expand agricultural production. But that remedy also has limitations. Too many people already compete for too little water. The aquifers of the world, on which so much agriculture in drier regions depends, are being drained of their groundwater faster than the reserves can be replaced by natural percolation of rainfall and runoff. The Ogallala aquifer, a principal water source of the central United States, experienced a three‐meter drop through a fifth of its area during the 1980s alone. Now it is half depleted beneath a million hectares in Kansas, Texas, and New Mexico. Still worse deficits are building in other countries, and often where they are least affordable. The water table beneath Beijing fell 37 meters between 1965 and 1995. The groundwater reserves of the Arabian peninsula are expected to be exhausted by 2050. In the meantime the oil‐rich countries there are making up the deficit in part by desalinizing seawater trading their precious petroleum for water. On a global scale, humanity is pressing the limit, using a quarter of the accessible water released to the atmosphere by evaporation and plant transpiration, and somewhat more than half that available in rivers and other runoff channels. By 2025, 40 percent of the world's population could be living in countries with chronic water scarcity. New dam construction can add 10 percent to the runoff capture during the next thirty years, but the treadmill opposing it is unceasing: In the same three decades the human population is expected to grow by a third.

As the land gives out, might we turn to Earth's last frontier, the boundless sea? Unfortunately, no, it is not really boundless, having already given most of what it has to offer. All seventeen of the world's oceanic fisheries are being harvested beyond their capacity. Only those in the Indian Ocean have continued to rise in yield, a trend destined to end because the present rate of catch is not sustainable. Several fisheries, including most famously the northwestern Atlantic banks and the Black Sea, have suffered a commercial collapse. The annual world fish catch, after rising fivefold from 1950 to 1990, has leveled off at about 90 million tons.

The history of marine fisheries has been one of increasingly efficient mass capture and on site processing, which increases yield by cutting ever deeper into existing stocks. By the 1990s proliferating fish farms had taken up part of the slack, adding 20 million tons to the total harvest. But aquaculture, the fin‐and‐shell revolution, also has limits. Expanding marine farms pre-empt the mangrove swamps and other coastal wetland habitats that serve as the spawning grounds for many offshore food fishes. Freshwater farms have more growth potential but must compete with conventional agriculture for the shrinking supplies of runoff and aquifer‐borne water.

Meanwhile, in accordance with the general principle of life that all large perturbations are bad, Earth’s ability to support the voracious human biomass is becoming even dicier through the acceleration of climatic change. During the past 130 years the global average temperature has risen by one degree Celsius. The signs are now strong—some atmospheric scientists say conclusive—that much of the change is due to carbon dioxide pollution. The connection is the greenhouse effect, in which carbon dioxide, along with methane and a few other gases, work like the glass enclosures used by gardeners. They admit sunlight but trap the heat generated by it. For the past 160,000 years, as tests of air bubbles in fossil ice show, the concentration of atmospheric carbon dioxide has been tightly correlated with the global average temperature. Now, boosted by combustion of fossil fuels and the destruction of tropical forests, the carbon dioxide concentration stands at 360 parts per million, the highest measure in the 160,000 year period.

now we leave the tarseal and hit the metal, continue here